Semiconductor workpieces are processed within process chambers. Many times, these process chambers are maintained at a pressure different, typically lower, than standard atmospheric pressure. In some embodiments, the pressure within a process chamber may be considered vacuum conditions, wherein the pressure in the chamber may be between 10−3 and 10−7 Torr. Maintaining this pressure requires adequate seals on all orifices and openings in the process chamber.
In addition, there are often payloads or mechanisms within the process chamber that are required to move. This movement may be accomplished using a shaft, actuated outside the process chamber, which penetrates at least one of the walls of the process chamber. FIG. 1 shows a typical embodiment, where the shaft 110 may enter the process chamber 100 through an opening in one of the walls 101. This shaft 110 may be able to move linearly in one direction, as shown by arrows 111, thereby changing the position of its payload 150 within the process chamber 100. This linear movement may be created by an actuator 130. This actuator 130 may be a linear motor, a ball screw, mechanical linkages or other suitable devices. In addition, the shaft 110 may be able to rotate, as shown by arrow 112, about its center axis. This may be done by incorporating a rotary bearing and rotary actuator (not shown) between the linear actuator and the shaft 110. In some embodiments, both linear motion 111 and rotary motion 112 are performed by the shaft 110. In other embodiments, only one of these types of motion is utilized. Thus, actuator 130 may be capable of linear motion 111, rotary motion 112 or both. An air bearing 120 may be used to maintain vacuum conditions within the process chamber 100. The air bearing 120 may be constructed as an annular ring, where the cylindrical shaft 110 enters the process chamber after passing through the central opening 123 in the ring. The air bearing 120 uses a layer of pressurized air delivered to its central opening 123 to position the shaft 110 and hold it in the desired position. Pressurized air is delivered through channels 121 in the air bearing 120, which terminate in the central opening 123 where the shaft 110 is disposed. The highly pressurized air serves to hold the shaft 110 in place, preferably so that the shaft 110 remains equally spaced from the sides of the central opening 123 of the air bearing 120. Thus, the air bearing 120 serves to align and support the shaft 110 throughout its range of motion in direction 111. In other words, the radial movement of the shaft 110 is minimized by the highly pressurized air which pushes against it in the central opening 123.
Additionally, the air bearing 120 may also have vacuum channels 122. These vacuum channels 122 are in communication with a vacuum pump (not shown) and serve to evacuate the pressurized air from the space in the central opening 123 so that this pressurized air does not enter the process chamber 100. In other words, the pressurized air in the volume between the air bearing 120 and the shaft 110, when used with vacuum channels 122 in communication with a vacuum pump, act as a seal, effectively isolating the external environment from the environment within the process chamber 100 and maintaining the desired pressure differential.
This configuration is useful in that the air bearing 120 serves two distinct purposes. First, it supports the shaft 110, using a nearly friction-less interface, and maintains its position within the central opening 123. Secondly, it provides a seal between the external environment and the process chamber 100, allowing a pressure differential to exist therebetween. However, in some embodiments, the weight or load associated with the shaft 110 or payload 150 may be too great to be supported by an air bearing 120. In this case, the highly pressurized air may not have enough load capacity to keep the shaft 110 properly aligned. Thus, the maximum weight of the payload 150 and the shaft 110 may be limited by the air bearing 120.
Therefore, it would be beneficial if there were an apparatus and method to allow a shaft and payload to penetrate a process chamber that does not impose limitations on the weight of these components. Furthermore, this apparatus should advantageously also provide the same sealing ability that is achieved by current air bearing systems.